In near field communications (NFC) systems, active beacons, unlike passive beacons, communicate with a reader via active load modulation (ALM), allowing significant increase in range and/or reduction in antenna seize. The beacon and reader carriers may be synchronized to avoid read errors at the NFC reader, and particularly to maintain compatibility with older amplitude modulation-only detecting readers, rather than new readers than can also detect phase differences. The signal that is observed at the beacon is an aggregate of the local carrier and reader-broadcast carrier, resulting in an offset that interferes with synchronization of the carrier frequency and phase.
The details of various embodiments of the methods and systems are set forth in the accompanying drawings and the description below.